In the past, certain papermakers' belts or fabrics have been described as being manufactured from porous cables comprising a plurality of monofilaments which are non-circular in cross-sectional configuration.In this connection, reference is made to Butler, U.S. Pat. No. 3,158,984. However, it is believed that such cabled structures would have several disadvantages which the present invention attempts to solve. For example, it is believed that such prior art structures would tend to stretch due to the void space encountered in the interstices of the cables making up the machine or longitudinal direction yarns of the fabric which interstices result from using such non-circular monofilaments. By machine or longitudinal direction yarns it is meant those yarns which extend in the direction of travel of such conveyor belt-like fabrics. In addition, it is believed that such structures would be subject to fill-up with pulp particles or fines or fillers in the interstices of the porous cables, thus causing the papermakers' belt to drain in a non-uniform manner. Further, due to the likelihood of pulp fines and fibers entangling and building up in the interstices present in the porous cables of such structures, it is believed that such belts would exhibit poor sheet release. By sheet release, it is meant the situation wherein the paper sheet is transferred from one section of a papermaking machine to another.
In the field of papermaker's fabrics it has also been known to make and use fabrics woven from traditional multifilament yarns which characteristically comprise a plurality of groups of twisted fibers or filaments. However, it is believed that in some papermaking applications such prior art fabrics have less dimensional stability in the cross-machine direction, and less desirable surface properties with regard to paper web formation, relative to the fabrics of the present invention. It is presently believed that these problems result from the structure of such prior art fabrics utilizing multifilament yarns made from fibers or filaments each of which has a cross-sectional diameter of 1.7 mils or less. While not wishing to be bound by any specific theory, it is thought that the constituents of the fibrous material in a multifilament yarn has a tendency to slide over one another, as for example, when tension is applied to the fabric. This sliding then causes the fabric to distort from the required shape causing sleasiness as well as other undesirable characteristics.
It is believed that it is possible to overcome the forementioned problems by utilizing a papermakers' belt which comprises yarns formed from circular monofilaments by which is meant monofilaments which are circular in cross-sectional configuration. Such yarns are plied or cabled such that essentially non-porous cables are formed. Without wishing to be bound by any particular theory, it is thought that by making a papermakers' belt having such non-porous cables it is possible to have a cabled structure with substantially no void space in the cables; hence reducing stretch when the belt is put on the drive rolls of a papermaking machine. It is also believed that by constructing a papermakers' belt utilizing monofilaments it is possible to overcome the sleasiness associated with prior are multifilament papermakers' belts. In addition, it is believed that the lack of avoids within the cabled structure of the belt of the present invention will prevent plug-up by pulp fines and fillers which might cause an irregular drainage surface or problems with regard to sheet release.
In addition to overcoming the forementioned problems, it is believed that papermakers' belts made in accordance with the teachings of the present invention provide a number of other advantages. For example, since such cabled yarns have a relatively high modulus of elasticity in addition to being non-porous, when they are used in the load bearing direction of a papermaker's belt it is possible to produce a belt having substantial stretch resistance. It is believed that this allows for the production of belts having low drag characteristics and therefore better wear characteristics, as well as an increase in the overall efficiency of the papermaking operation. The term drag as used herein is meant to refer to the frictional interaction between the papermakers' belt and the surfaces of the papermachine components. Further, by weaving with such cabled structures as in the present invention, it is possible, if desired, to increase the number of cross-machine direction strands or cables per inch without reducing the number of machine direction cables per inch unless such a reduction is desired. By so increasing the number of cross-machine direction strands or cables per inch it is possible, if desirable, to produce a fabric having square interstices without having to reduce the number of machine direction cables per inch to effect such a result. Unexpectedly, it has been found that such fabrics have excellent pulp fine retention properties as well as superior cross machine direction stability and shove resistance. By shove resistance it is meant the ability of adjacent yarns or cables to maintain their position relative to one another when lateral forces act on their side walls. It is thought that the improved fine retention properties results from the use of a fabric having square interstices.
Without wishing to be bound by any particular theory, it is believed that a greater number of cross machine direction strands or cables can be included in fabrics as described above because prior to finishing the machine direction cables of the present invention have a relatively high degree of deformability, thus allowing more cross machine direction strands or cables to be inserted for a given unit of belt width. Hence, using such cables not only allows for the introduction of a greater number of cross machine direction strands or cables in the fabric but also enables the manufacturing of such fabrics at lower loom loads than would otherwise be possible without the use of such cables. It is thought that lower loom loads can be utilized because such cables are easily deformable before finishing and hence give less resistance to forces exerted during weaving.
Thus, it is an object of the present invention to provide a papermaker's belt in which non-porous cables extend in the machine direction and are comprised of yarns formed from monofilaments which are circular in cross-sectional configuration.
It is a further object of this invention to provide a papermakers' belt having improved stretch resistance in comparison to prior art papermaker's fabrics.
Another object of the present invention is to provide a papermakers' belt which provides for improved retention of pulp fines.
A still other object of this invention is to provide a means of increasing the number of cross machine direction strands or cables per inch in a papermakers' fabric without reducing the number of machine direction cables per inch while utilizing low loom loads.
A further object of the present invention is to provide a papermakers' belt having improved dimensional stability and shove resistance.
A still further object of the present invention is to provide a papermakers' belt having improved drainage uniformity.
Another object of the present invention is to provide a papermakers' belt having improved sheet release properties.
Yet, another object of the present invention is to provide a papermakers' belt having reduced pulp fine and filler build-up in the cables comprising the belt.